1. Field of the Invention
This invention relates to a sprocket assembly for a bicycle, more particularly to a speed varying sprocket assembly with chain guiding means for smoothing transmission of a driving chain between the sprocket wheels of the assembly.
2. Description of the Related Art
In this art, a speed varying sprocket assembly consists of two or more sprocket wheels containing a different number of teeth which are combined for mounting to a rear hub or front crank. The driving chain is shifted axially of the sprocket wheels through a derailleur so as to be switched to a selected one of the sprocket wheels. In a case where a driving chain is shifted from a sprocket wheel smaller in diameter and number of teeth to one larger in diameter and number of teeth, when passing through a point located right in the middle of the space defined between an adjacent pair of inner link plates of the driving chain, the tip of a sprocket tooth may be brought into contact with the leading edge of the lagging one of the adjacent pair of inner link plates due to the fact that the adjacent pair of inner link plates are spaced from each other at a small distance, thus hindering the chain from meshing quickly and smoothly with the teeth. As a result, the meshing of the driving chain with the sprocket wheel is slow, causing idling or the generation of noise between the chain and the sprocket wheel.